Erythrocyte membrane glycoprotein Band 3 (molecular weight approximately 93 kilograms) is being studied. A fraction of Band 3 that is (32P)-phosphorylated less than normal controls has been identified in patients with myotonic muscular dystrophy (MyD). We propose to develop alternate methods of Band 3 purification using recently described procedures and to develop fraction specific antibodies to Band 3 for use in purification schemes. Purification of Band 3 in sufficient yield and purity will allow quantitative analysis and use in peptide mapping experiments comparing MyD and control Band 3. Clinically relevant genetic and diagnostic considerations may be more rationally approached using data from these experiments.